Driving assistance communication systems are known. Such systems are used to allow vehicles to move around more smoothly. In a driving assistance communication system, vehicles wirelessly transmit vehicle information including their driving state to other vehicles and wirelessly receive the vehicle information from other vehicles. With this system, for example, a vehicle at an intersection can acquire information on other vehicles approaching the intersection from blind spots, and can avoid contacting the other vehicles.
The driving assistance communication system needs to make sure that the vehicle information communicated among vehicles is not falsified information, and that the vehicle information is not transmitted from a spoofed source address. Thus, the vehicle information communicated in the driving assistance communication system includes verification information for ensuring validity, such as integrity of information and authenticity of a transmission source. The verification information is, for example, a message authentication code using a shared key encryption system or a digital signature using a public key encryption system. A transmitter vehicle adds the verification information to the vehicle information. A receiver vehicle verifies the vehicle information on the basis of the added verification information.
In the driving assistance communication system, two or more vehicles broadcast the vehicle information on the same channel (the same frequency band). This configuration requires more processing capability of a communication device installed in each of the vehicles in receiving information than that in transmitting information.
For example, the communication device broadcasts a combination of the vehicle information and the verification information predetermined times per second, such as 10 times per second. The communication device also receives the combination of the vehicle information and the verification information from each of the vehicles that are present therearound. Thus, the communication device needs to receive the combination of the vehicle information and the verification information the number of times equal to the transmission frequency per second multiplied by the number of vehicles present therearound. When, for example, 100 vehicles are present therearound, the communication device needs to receive the combination of the vehicle information and the verification information 1000 times per second.
Verification processing accounts for a relatively large proportion of the overall reception processing. Thus, the driving assistance communication system is required to reduce the load of the verification processing performed in each vehicle on the vehicle information.